A phase-locked loop (PLL) is sometimes formed using a ring oscillator with inverters annularly connected together. Ring oscillators are sensitive to disturbance, and thus a bandlimiting filter for narrow bands is provided in a frequency coarse-tuning circuit, a bias circuit, or the like in a PLL.
For example, such a PLL is expected to be incorporated into a system (or an apparatus) that intermittently operates a power source. In this case, the bandlimiting filter for narrow bands may increase lockup time following power-on. The increased lockup time prevents the data rate of the system from being improved.